Emplois, stages

The objective of the PLATO space mission (ESA), which will be launched towards the end of 2026, is to measure the flux of many stars in order to detect possible occultations associated with the passage of (rare) Earth-like planets located in the so-called ’habitable zone’ (technique of transits). Once detected, the planets will be characterize by measuring their masses and radii. Those measurements can be done only with respect ot the masses and radii of their host star which need therefore to be characterized as well by means of seismic studies. Both techniques require photometric measurements of very high precision and temporal stability.

Photometric measurements will be based on CCD (Charge Coupled Devices) detectors placed at the focus of each telescope (26 telescopes in total). For a large number of stars, photometric measurements will be carried out on board using masks centred on the stars of interest, whereas for the brightest stars, they will be carried out on the ground using thumbnails that will be regularly acquired on board and transmitted to the ground. All the data acquired on board will undergo a certain amount of processing and correction on the ground. These will be applied by a pipeline that will produce light curves ready for scientific analysis. These light curves will be analysed by a scientific pipeline called the Stellar Analysis System (SAS). In a first step, a seismic analysis will provide the seismic parameters of the stars. In a second step these seismic parameters will be used by a stellar analyse process to provide masses, radii and ages of the host stars.

The on-ground processing chains for the raw mission data include a calibration part (in particular the modelling of the Point Spread Function - PSF), a photometric reduction part of the images and finally a part dealing with the correction of the on-board generated light curves. The definition of the associated algorithms is already well underway, and the PLATO Data Processing Algorithm Working Group (DPA-WG) is in the process of writing the so-called Algorithm Theoretical Baseline Definition (ATBD) documents. These documents will be delivered with the prototype codes and associated unit test sets. These materials will then be used by other PLATO Data Center teams (PDC, WP33) to develop the processing chains (onboard and ground). In this context, the work will consist on developing the simulation sets using the PLATOSim simulator (Marcos-Arenal et al, 2014) as well as some appropriated simulation tools and scripts. Concerning the scientific analysis, the work will consist in defining - in collaboration with the experts- the test cases representing the thousands of stars (signal to noise, type of star) that PLATO will observe . Then for each test, simulations of the expected light curve will be built for observation periods of three months to two years. These simulated light curves will be generated with the PLATO Solar-like Light-curve Simulator (PSLS, https://sites.lesia.obspm.fr/psls/ ; Samadi et al 2019). These simulations will be used to test the very complex prototype stellar analysis chain (SAS) that will provide the masses, radii and ages of PLATO stars. The architecture of the SAS stellar analysis chain is already defined and the prototype is almost built. Simulations will quickly be necessary to test in particular the different connections and the different options of the analysis chain according to the star considered and the assumed signal-to-noise ratio.

References : - Rauer et al, 2014, Experimental Astronomy, 38, 249 - Marcos-Arenal et al, 2014, A&A, 566, A92 - Samadi et al, 2019, A&A, 624A, 117S - Marchiori et al 2019, A&A, 627A, 71M - Reese, D. R. et al, 2016 A&A 592, 14 - Silva Aguirre, V et al ., 2017ApJ 835., 173  Technical notes directly related to this job can be provided on-demand.

To carry out the work we are looking for someone with skills/expertise in both computer science and general physics (more specifically -if possible- in the field of instrumentation and general astrophysics). The candidate must hold a doctorate in astrophysics (or in a similar subject : physics, or signal processing for example) or an engineering degree (including experience in astrophysics research or signal processing). The person will have experience in software writing and/or data analysis. A good knowledge of written and oral English is essential. Previous work experience in a context related to space research would be a plus. Experience in image data analysis and / or optics will be much appreciated. Knowing the Python and C/C ++ languages would be a plus, as well as a practice of collaborative development tools (e.g. Git).

The position will take place at LESIA-Observatoire de Paris, at the Meudon site (92, Haut de Seine, France). The candidate must appreciate teamwork and agree to travel within Europe to visit different partners, if sanitary conditions allow it. Depending on the sanitary situation next September, it is possible that the work will first start in a hybrid way (partly remote and partly face-to-face), which may make the training phase less optimal. The position is initially for one year and is renewable for an additional year. The position is open at the earliest from September 2021. The application must be submitted here : https://emploi.cnrs.fr/Offres/CDD/UMR8109-SYLDES-031/Default.aspx Applications are being solicited now and a first review will be conducted starting from the beginning of June.